In the field of video cameras, as a video signal processing apparatus and a video signal processing method for performing knee processing on signals of three primary colors captured with an image pickup device such as CCD or the like, there is a conventional contrivance as described in Japanese Laid-open Patent Publication No. H9-238359.
The above-cited conventional video signal processing apparatus performs knee processing on each of R (Red) G (Green) B (Blue) primary color signal (R signal, G signal, and B signal) captured with a respective CCD which constitutes a 3CCD image pickup medium, and then generates luminance signals and color difference signals based on the signals which have been subjected to the knee processing.
FIG. 1 is a block diagram illustrating the configuration of a conventional video signal processing apparatus 10. As illustrated in FIG. 1, each primary color signal (R signal, G signal, and B signal) fed from an image pickup device is inputted into a respective gamma correction circuit 11a, 11b, and 11c corresponding to each color signal. Gamma correction circuit 11a performs gamma correction processing on R signals in accordance with the luminescent characteristics of a display apparatus such as a CRT (Cathode Ray Tube) or the like.
Knee circuit 12a performs non-linear signal compression processing on signals outputted from gamma correction circuit 11a, where such processing is targeted at signals exceeding a certain predetermined level, thereby narrowing a wide dynamic range of natural light down to a narrower dynamic range for video signals. The signals subjected to dynamic range compression at knee circuit 12a are provided to corresponding white clip circuit 13a and color difference signal generation circuit 15.
White clip circuit 13a performs white clip processing on signals outputted from knee circuit 12a, where such processing is targeted at signals exceeding a certain predetermined level, and provides the white-clipped signals to luminance signal generation circuit 14.
Meanwhile, gamma correction circuit 11b performs gamma correction processing on G signals in accordance with the luminescent characteristics of the display apparatus such as a CRT or the like. Knee circuit 12b performs non-linear signal compression processing on signals outputted from gamma correction circuit 11b, where such processing is targeted at signals exceeding a certain predetermined level, thereby narrowing a wide dynamic range of natural light down to a narrower dynamic range for video signals. The signals subjected to dynamic range compression at knee circuit 12b are provided to corresponding white clip circuit 13b and color difference signal generation circuit 5.
White clip circuit 13b performs white clip processing on signals outputted from knee circuit 12b, where such processing is targeted at signals exceeding a certain predetermined level, and provides the white-clipped signals to luminance signal generation circuit 14.
Further meanwhile, gamma correction circuit 11c performs gamma correction processing on B signals in accordance with the luminescent characteristics of the display apparatus such as a CRT or the like. Knee circuit 12c performs non-linear signal compression processing on signals outputted from gamma correction circuit 11c, where such processing is targeted at signals exceeding a certain predetermined level, thereby narrowing a wide dynamic range of natural light down to a narrower dynamic range for video signals. The signals subjected to dynamic range compression at knee circuit 12c are provided to corresponding white clip circuit 13c and color difference signal generation circuit 5.
White clip circuit 13c performs white clip processing on signals outputted from knee circuit 12c, where such processing is targeted at signals exceeding a certain predetermined level, and provides the white-clipped signals to luminance signal generation circuit 14.
Luminance signal generation circuit 14 generates luminance signals Y based on signals provided from white clip circuits 13a, 13b, and 13c. On the other hand, color difference signal generation circuit 15 generates color difference signals R−Y and B−Y by performing matrix processing based on signals provided from knee circuits 12a, 12b, and 12c. 
Luminance signals Y generated by luminance signal generation circuit 14 and color difference signals R−Y and B−Y generated by color difference signal generation circuit 15 are provided to the display apparatus such as a CRT or the like.
In this way, according to conventional video signal processing apparatus 10, knee processing is performed separately on each primary color signal (R signal, G signal, and B signal) captured with an image pickup medium.
On the other hand, as another conventional video camera, there is a single CCD type camera which has a configuration in which either a primary color filter [R (Red), G (Green), B (Blue)] or a complementary color filter [Ye (Yellow), Mg (magenta), G (Green), Cy (Cyan)] is provided on the incident plane of one CCD correspondingly to pixels, and which generates luminance signals Y and color difference signals R−Y and B−Y based on color signals subjected to photoelectric conversion through either one of these color filter.
Such a single CCD type video camera employs just one CCD image pickup device, which has an advantage of ensuring a small size of an optical system and achieving a compact configuration of the video camera as a whole. Generally, knee processing is performed in this single CCD video camera, too.
However, according to conventional single CCD video cameras, either primary color signals or complementary color signals (hereafter collectively referred to as video signals) before generation of luminance signals and color difference signals are respectively subjected to color signal processing such as gamma correction, knee processing, white clipping, and so on, and accordingly, for example in a case where video signals containing a portion which exceeds a certain signal level which serves as a threshold as to whether signal compression processing is performed or not in knee processing (a knee point, that is, a reference point in knee processing) also contain a portion which does not exceed the knee point, knee processing characteristics will differ depending on whether the level of the signal exceeds the knee point or not.
In this way, when portions having different knee processing characteristics exist in a series of video signals, a problem arises; it becomes difficult to adequately generate color components when generating a color component from a difference in the signal level between each sequential pixel of the video signals subjected to knee processing.
In addition, also in a case where sequential two pixels of video signals captured with a CCD image pickup device are added up to be used for generation of luminance signals, supposing that an imaging object having a video signal level over a knee point contains some pixels whose level do not exceed the knee point, knee processing characteristics will differ depending on whether a level exceeds the knee point or not. Consequently, when it is attempted to generate luminance signals based on video signals after knee processing, in some cases, it could be difficult to acquire accurate luminance signals, which would result in a problem called a differing line concentration in which a luminance level varies from line to line even for the same imaging object.
Furthermore, in a case where flaw correction is performed after generation of luminance signals and color difference signals from output signals of a CCD image pickup device, because a filtering processing associated with the generation of the luminance signals and the color difference signals has been performed, a flaw has been spread into surrounding pixels, which results in a conventional problem of a greater difficulty in achieving a flaw detection in an appropriate manner, and the provisioning of flaw correction circuits respectively for the luminance signals and the color difference signals leads to a further conventional problem of an increased circuit scale.